The present invention relates to the manipulation of optical signals and, more particularly, to thermally-induced free-space optical switching.
Switches are needed in optical communications networks for, e.g., routing optical signals. Several types of optical switches have been proposed, each with its own set of advantages and disadvantages.
Mechanical switches, such as those with a moving prism and lens, have small wavelength dependent loss, low loss, and operate in free-space, but are complex, expensive to manufacture, and questionable long-term reliability.
Several integrated optical switches, which take advantage of integrated semiconductor fabrication techniques, have been proposed. Typically, in such integrated optical switches, waveguides are formed on a substrate and a change in refractive index of the waveguide material is induced to control light switching. Such integrated optical switches have several drawbacks. Integrated optical switches based on an electro-optical effect or electromagnetic effect are polarization dependent and usable only for single-mode light. Switches that rely upon refractive index changes induced by injection of charge carriers suffer from high losses due to carrier absorption.
Regardless of the mechanism by which the change in refractive index is induced, integrated optical switches require light to be coupled first into a waveguide. Such waveguides are typically on the order of 10 xcexcm or less in width, making the coupling of light into an integrated optical switch a non-trivial procedure.
The present invention provides an optical device that employs thermally induced total internal reflection to alter a light beam propagating in free-space without using moving parts. The thermo-optical device of the present invention has a first material having a first refractive index and a second material having a second refractive index. The first and second materials are in contact with each other to form an interface. At a first temperature, the second refractive index is substantially equal to the first refractive index, and the light beam is transmitted through the interface. At a second temperature at which the second refractive index is different than the first refractive index, at least some of the light beam is reflected at the interface.